Thysania agrippina, above, has many common names, the Birdwing moth, the ghost moth, the Great grey witch, and the Great owlet moth. At 27 - 28 cm it has the biggest wingspan of any moth, and one individual reportedly reached 30 cm.
It is found in Mexico, Central and South America, and sometimes as far north as Texas.
The female lays her eggs in loosely spaced groups or singly on or near the foodplant, which is the India rubber tree, Hevea brasiliensis. The eggs hatch in April.
The grey dagger is common throughout Europe and the British isles, and found in most habitats especially woodlands, hedgerows and gardens. There is one generation a year, though there may be 2 generations in the south.
Eggs are laid singly on the foodplant (see caterpillar) leaves in July or August, and hatch in a week.
The caterpillar (see above) is blue/grey with a yellow stripe down its back, and white below the spiracles, red spots above, a black head, a spike on its back just after the true legs, and another spike or hump just before the last pair of prolegs. Foodplants include birch, alder, hawthorn, blackthorn, plum, pear, apple, and many others. Length is up to 38 mm. They feed from August until October.
They pupate in a silk cocoon in the cracks of bark, in rotten wood or in the soil.
Adults emerge the following year in June. Adult length at rest is 17 - 20 mm, and the wingspan is 30 - 42 mm. It is very similar to the Dark dagger, Acronicta tridens.